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Matt Joyce Will Improve Versus Lefties With Sample Size

No need for a cutesy intro here as it’s just a continuation of Matt Joyce day on TPR. Two thoughts prevail from the news about his select playing time against left-handed pitching:

1) His numbers will improve with more playing time against lefties
2) Using him against all lefties is sub-optimal

I agree with both lines of thought.

In Joyce’s big league career, he has 60 plate appearances versus lefties in which he’s hit .157/.267/.235. Last season, left-handed batters hit .242/.313/.370 off their same-handed counterparts (righties hit .254/.313/.397 versus theirs). The Book tells us we need 1,000 plate appearances from lefties versus lefties to regress 50 percent of the way to league average. Suffice to say, Joyce is a wee bit off that total. Using the formula r=PA/(PA+1000) one can discover Joyce has to be regressed roughly 94% towards league average to get a grip on his true talent level versus lefties, like this:

You could it a step further and regress Joyce with a group of lefties who are similarly good against righties (Joyce has an OPS over .850 in more than 500 plate appearances) and so on, but the larger point to take away is that Joyce is going to improve versus lefties because he is a good hitter. The idea about him improving from seeing more lefties is actually valid because the larger the sample size, the more true talent level will leak through which – in this case – represents an improvement. In some cases, this would not be an improvement. Simply becoming more familiar with pitchers of a certain hand does not guarantee better results, otherwise we’d expect Joyce to continue to hit righties better too and while he may, we expect that to be gradual and on line with a typical aging curve, not radical like his progress versus lefties is charted.

With all that about Joyce’s given improvement written, the Rays still shouldn’t go out of their way to play him against lefties, not with better options versus lefties available. Carl Crawford played against lefties constantly. Over his first three seasons, he managed a .649 OPS. Over his last three with the Rays? He managed a .685 OPS. Crawford did not have as far to go towards league average as Joyce, but he wound up just above league average. Joyce probably will too – with or without the 597 plate appearances Crawford got in between.

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[…] RJ Anderson at The Process Report writes that Matt Joyce will improve against lefties just by increasing his (at bats). Do not be intimidated by concepts like “regression” or “sample size.” I let the math in posts like this scare me away for too long. This is fundamentally interesting stuff. […]